[mediaqueries] temporary doc to hold features deferred to MQ5.

mediaqueries/deferred-for-level-5.txt

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+
+<h2 id='mf-environment'>
+Environment Media Features</h2>
+
+<h3 id="light-level">
+light-level</h3>
+
+	<pre class='descdef mq'>
+	Name: light-level
+	Value: dim | normal | washed
+	For: @media
+	Type: discrete
+	</pre>
+
+	The 'light-level' media feature is used to query about the ambient light-level in which the device is used,
+	to allow the author to adjust style of the document in response.
+	The following values are valid:
+
+	<dl dfn-type=value dfn-for="@media/light-level">
+		<dt><dfn>dim</dfn>
+		<dd>
+			The device is used in a dim environment,
+			where excessive contrast and brightness would be distracting or uncomfortable to the reader.
+			For example: night time, or a dimly illuminated indoor environment.
+
+		<dt><dfn>normal</dfn>
+		<dd>
+			The device is used in a environment with a light level in the ideal range for the screen,
+			and which does not necessitate any particular adjustment.
+
+		<dt><dfn>washed</dfn>
+		<dd>
+			The device is used in an exceptionally bright environment,
+			causing the screen to be washed out and difficult to read.
+			For example: bright daylight.
+	</dl>
+
+	User agents should set the thresholds between the three levels
+	in a way that takes into account the characteristics of the device.
+
+	<div class="note">
+		Even though it is expected that User Agents will adjust the value of this media feature
+		based on ambient light sensors,
+		this specification intentionally refrains from defining the three levels in terms of a measurement in lux,
+		for several reasons:
+
+		<ul>
+			<li>
+				Devices equipped with a light sensor usually adjust the brightness of the screen automatically.
+				Depending on the level of adjustment,
+				the thresholds for needing a low contrast or hight contrast content may vary.
+
+			<li>
+				Different screen technologies wash out at very different ambient light levels;
+				e-ink displays remain readable in bright daylight,
+				while liquid crystal displays do not.
+
+			<li>
+				Many embedded light sensors are inaccurately calibrated,
+				making it difficult to establish useful thresholds valid across devices.
+		</ul>
+	</div>
+
+	For accessibility purposes, user agents may offer manual controls
+	allowing the user to switch between the three levels of independently of the ambient light level,
+	as high contrast or low contrast styles may be more suitable for users with visual disabilities.
+
+	<p class="issue">
+		Using this media feature for accessibility purposes overlaps a lot with <a href="http://msdn.microsoft.com/en-us/library/windows/apps/hh465764.aspx">the high-contrast media feature proposed by Microsoft</a>.
+		Can we adjust this so that it covers all use cases for both,
+		or somehow modify them to work in an orthogonal, rather than overlapping, fashion?
+
+	<div class="example">
+		<pre>
+		@media (light-level: normal) {
+			p { background: url("texture.jpg"); color: #333 }
+		}
+		@media (light-level: dim) {
+			p { background: #222; color: #ccc }
+		}
+		@media (light-level: washed) {
+			p { background: white; color: black; font-size: 2em; }
+		}
+		</pre>
+	</div>